title: Constitutive expression of the GIGANTEA ortholog affects circadian rhythms and suppresses one-shot induction of flowering in Pharbitis nil, a typical short-day plant.
abstract: GIGANTEA (GI) is a key regulator of flowering time, which is closely related to the circadian clock function in Arabidopsis. Mutations in the GI gene cause photoperiod-insensitive flowering and altered circadian rhythms. We isolated the GI ortholog PnGI from Pharbitis (Ipomoea) nil, an absolute short-day (SD) plant. PnGI mRNA expression showed diurnal rhythms that peaked at dusk under SD and long-day (LD) conditions, and also showed robust circadian rhythms under continuous dark (DD) and continuous light (LL) conditions. Short irradiation with red light during the flower-inductive dark period did not change PnGI expression levels, suggesting that such a night break does not abolish flowering by affecting the expression of PnGI. In Pharbitis, although a single dusk signal is sufficient to induce expression of the ortholog of FLOWERING LOCUS T (PnFT1), PnGI mRNA expression was not reset by single lights-off signals. Constitutive expression of PnGI (PnGI-OX) in transgenic plants altered period length in leaf-movement rhythms under LL and affected circadian rhythms of PnFT mRNA expression under DD. PnGI-OX plants formed fewer flower buds than the wild type when one-shot darkness was given. In PnGI-OX plants, expression of PnFT1 was down-regulated, suggesting that PnGI functions as a suppressor of flowering, possibly in part through down-regulation of PnFT1.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Higuchi
authors.forename: Kimiyo
authors.initials: K
authors.lastname: Sage-Ono
authors.forename: Ryuta
authors.initials: R
authors.lastname: Sasaki
authors.forename: Namie
authors.initials: N
authors.lastname: Ohtsuki
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hoshino
authors.forename: Shigeru
authors.initials: S
authors.lastname: Iida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kamada
authors.forename: Michiyuki
authors.initials: M
authors.lastname: Ono
mesh_terms: D029681:Arabidopsis Proteins / Q000235:genetics; D001483:Base Sequence; D002940:Circadian Rhythm / Q000235:genetics* / Q000528:radiation effects; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D003624:Darkness; D015536:Down-Regulation / Q000235:genetics; D035264:Flowers / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D049915:Ipomoea nil / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D008027:Light; D008969:Molecular Sequence Data; D017440:Photoperiod; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D017422:Sequence Analysis, DNA; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D018744:DNA, Plant; D004268:DNA-Binding Proteins; C418905:FT protein, Arabidopsis; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant